Heliograph

Description

The first heliograph known as “heliograph Campbell-Stokes” was manufactured by Campbell in 1853.

It consisted of a Boule of crystal 10 cm in diameter, exposed to the Sun, serving as lens concentrating the radiation Infrarouge Sun, while attenuating it more than a Loupe, so as to burn a sheet of special Papier rigid placed at a judicious distance under the ball on a curved support.

The support of paper makes it possible to move this last according to the Saison, i.e. the maximum height of the Sun to the top of the horizon. The burned part of the sheet of paper indicated the moments of the day when the Sun had been shining without Nuage S.

The Lumière burns paper progressively displacement of the focal point, as long as the Sun is shining.

The paper band is graduated in hours, or more finely. Measurement is vague in Hiver and when the Sun is filtered by clouds which block the infra-red. The system does not function with the paddle and the setting where the infra-red is filtered by the atmosphere.

A graduation of the serrated rollers makes it possible to regulate the slope of the support according to the Latitude of the point where the heliograph is installed.

Since, automatic systems equipped with electric eyes, or other types of materials are used.

One distinguishes:

static heliographs: they comprise two photovoltaic cells of which one measures the total Rayonnement and the other the diffuse radiation. If the Sun is present, this system with two cells delivers a signal of imbalance starting from a given threshold.
dynamic heliographs; equipped with a moving part, they can analyze the difference between Luminance sky and that of the Sun.

The Solarigraphe S use the thermoelectric couples formed by the superposition of Thermocouple S assembled in series to produce a Electric current proportional to the received radiation.

Certain systems are designed to measure the light which arrives on the ground through the Canopée.

Utility

The knowledge of the duration of sunning is useful in Météorologie, but also for the energeticians (for calculations of production of warm water or electricity by solar panels or fitteds carpet for example), like for the ecologists (the light being the condition of the Photosynthèse).

Similar systems were imagined to guide mobile solar panels towards the sun.

There exist also Spectrohéliographe S, equipped with filters and Caméra S which selects some wavelengths, in order to study for example:

the solar activity, of which the eruptions and protuberances (dynamic pre-eruptive and eruptive, which can have impacts on the radio weather and transmission),
the dynamics of the solar filaments.

Calculation of precise sunning on line on www.sun-time.org

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